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4.3.6
Condenser Pressure Control
When configuration variable CnF14 is set to "In" the condenser pressure control logic is activated to maintain dis-
charge pressures above 130 psig in low temperature ambients. The logic turns the condenser fan on or off in
accordance with the condenser pressure transducer reading. (Refer to
the following conditions are met:
1. The ambient sensor reading is less than or equal to 27°C (80°F)
2. Voltage/Frequency ratio is less than or equal to 8.38
When the above conditions are met, either pressures or timers may dictate a change of state from OFF to ON, or
ON to OFF. If the condenser fan is OFF, it will be energized if saturated condensing pressure is greater than 200
psig OR if the condenser fan has been OFF for a variable time period of up to sixty seconds depending on the
ambient temperature. As the ambient temperature increases, the amount of time that the condenser fan is ener-
gized will correspondingly increase towards the maximum.
If the condenser fan is ON, it will de-energize only if the saturated condensing pressure is less than 130 psig and
the condenser fan has been running for a minimum of thirty seconds depending on the ambient temperature.
4.3.7
Arctic Mode
With arctic mode enabled, (configuration variable CnF29 set to "In") there will be a 30 minute time delay at startup
if the ambient is colder than -10.0°C. (14 5F) When the START/STOP switch is placed in the "I" (ON) position the
controller will energize the compressor crankcase heater. Operation of the heater will warm the oil and boil off any
liquid refrigerant that may be present in the crankcase.
If Pre-Trip is initiated during the 30 minute time period, Pre-Trip will be allowed to run normally. Once Pre-Trip is
over, the controller will revert to its normal control mode logic. Refer to
4.3.8
Perishable Mode - Conventional
The unit is capable of maintaining supply air temperature to within 0.25°C (0.5°F) of set point. Supply air tempera-
ture is controlled by positioning of the suction modulation valve (SMV), cycling of the compressor and cycling of the
heaters.
When pulling down from a temperature that is more than 5°C (9°F) above set point, the SMV will open to reduce the
pulldown time. However, pressure and current limit functions may restrict the valve, if either exceeds the preset value.
The Operational Software is designed so the SMV will begin to close as the set point is reached. The SMV will con-
tinue to close and restrict refrigerant flow until the capacity of the unit and the load are balanced.
If the temperature drops below the set point, the compressor will remain running for a few minutes. This is to
accommodate any initial undershoot which might occur. After this time has expired and the temperature is 0.2°C
(0.4°F) or greater below the set point, the compressor will be turned OFF.
If the temperature drops to 0.5°C (0.9°F) below set point, the heaters will be energized. The heaters will de-energize
when the temperature rises to 0.2°C (0.4°F) below the set point. The compressor will not restart until the temperature
rises to 0.2°C (0.4°F) above the set point and three minutes have elapsed since the last compressor turn off.
4.3.9
Perishable Mode - Economy
The economy mode is an extension of the conventional mode and is applicable to units with two speed evaporator
fan motors. The mode is activated when the setting of function code Cd34 is "ON". Economy mode is provided for
power saving purposes. Economy mode could be utilized in the transportation of temperature tolerant cargo or non-
respiration items which do not require high airflow for removing respiration heat. There is no active display indicator
that economy mode has been activated. To check for economy mode, perform a manual display of code Cd34.
In order to achieve economy mode, a perishable set point must be selected prior to activation. When economy
mode is active, the evaporator fans will be controlled as follows:
At the start of each cooling or heating cycle, the evaporator fans will be run in high speed for three minutes. They
will then be switched to low speed any time the supply air temperature is within 0.25°C (0.45°F) of the set point and
the return air temperature is less than or equal to the supply air temperature +3°C (5.4°F). The fans will continue to
run in low speed for one hour. At the end of the hour, the evaporator fans will switch back to high speed and the
cycle will be repeated.
T-316
Table
4–4.) The function is enabled when
Table
4–4.
4–6
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